I mean, you can run gii to update your model codes in your "protected/models" directory.
I don't delete any code. I just delete "db schema caches" in "protected/runtime/cache".
You must not touch any codes under the "framework" directory.

I changed my DB and in Gii I updated the model but without rewrite my model's file, because I have made lots of changes on model's file and the change in DB was small, so added this little change in my model's file's code. All went fine doing in this way.